In-vivo flow fields

The flow field experienced by a liquid as it is ingested is complex. For the few seconds that the liquid is in the mouth, it obviously experienced shear flows, but also as the tongue is pressed against the pallet, or when the liquid flows aroimd the mouth and moved through small orifices it also encotmters extensional flow. For simple non-Newtonian liquids, the average shear rate in the mouth has been estimated as 50 s-i the typical extension rates are siirdlar. 

The interaction between these flow fields and the perceived experience of eating and drinking is complicated, but it is possible to relate verbal descriptors such as creamy or thick to measured rheological properties. 

A high degree of viscoelasticity—experienced as stringiness—is obviously imacceptable to consumers, but some viscoelasticity is inevitable, given the kinds of high molecular-weight polymers such as proteins that are dissolved in the aqueous phase. 

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